Many current printers do not directly monitor the position of the paper relative to the print head, but rather rely upon encoders on the paper feeder roller and on the print head carriage. Such an approach places a higher burden on printer mechanics to effect paper registration, and also limits printing resolution.
Using an imager similar to those found in some optical mice to provide closed loop feedback during printing is also known. Previous efforts along these lines ran into difficulties, however, mainly due to accumulated error. That is, while absolute position of a sheet of paper in a printer might be known initially by referencing, for example, the upper left-hand corner of the sheet, as printing progresses slight errors from frame to frame can accumulate and result in significant offset between true and calculated paper positions.
One way to overcome problems associated with accumulated errors is to is use pre-printed paper, such as that provided in the ANOTO™ digital pen system (see, for example, http://www.anoto.com/?id=906). Unfortunately, not only is special paper required in such a system, but registration landmarks disposed on the paper may be visible, which detracts from the perceived quality of the printed output.
What is need is a printing registration system that is not expensive, commercially viable, accurate, permits high-speed printing, and that does not accumulate positional errors.